Symbian on Bluetooth® wireless technology

Overview

The Personal Area Network (PAN) will be a key feature of mobile phones and Bluetooth® wireless technology will be the enabling technology. The Bluetooth® Special Interest Group (SIG) has more than 1700 members representing a broad spread of industry interest. That makes it the fastest growing industry standard ever. With such potential, it is not surprising that many of Symbian's licencees see Bluetooth® wireless technology as a central mobile phone technology. Mal Minhas, PAN System Architect at Symbian explains how Bluetooth® wireless technology support for Symbian OS is being implemented.

Bluetooth® wireless technology is an open specification for wireless communications of data and voice. It is based on a low-cost short-range radio link which operates on a globally-available radio frequency.

Bluetooth® wireless technology will enable users to connect their computers, mobile phones, handheld devices, network access points and other devices via wireless short-range radio links unimpeded by line-of-sight restrictions.

Some of the features of Bluetooth® wireless technology are:

Signals can be transmitted through walls and briefcases, thus eliminating the need for line-of-sight.
Devices do not need to be pointed at each other, as signals are omni-directional.
Both synchronous and asynchronous applications are supported, making it easy to implement on a variety of devices and for a variety of services, such as voice and Internet.
Devices have a range of about 10 metres and up to eight devices can link to form a piconet. Piconets communicate with each other easily and the chips can change frequency at about 1600 hops per second. This phenomena is known as frequency hopping, and provides protection against interference.
Governments world wide regulate it, so it is possible to utilise the same standard wherever one travels.

Eliminating the need for proprietary cables to connect devices, Bluetooth® wireless technology will increase the ease and breadth of wireless connectivity. Connection cables will become obsolete - Bluetooth® wireless technology will allow users to establish ad-hoc connections between a variety of devices, creating networks and links wherever they go.

Application development on Symbian OS

Symbian OS is a 32-bit multi-tasking operating system that is specifically designed for portable, battery-powered mobile phones. Some of the key features that make Symbian OS ideal for developing communications software include:

A flexible client-server based architecture and programming systems to support compact but powerful software on wireless information devices.
Instant access to user data using an effective multi-tasking kernel at the lowest-level, and a very easy user interface framework at the highest level.
Robust software design achieved through component-based object orientation and comprehensive use of design patterns and frameworks.
Adaptability to different device types and different underlying communication technology.

C++ and Java software development kits.

At the heart of Symbian OS comms functionality lie two servers, the socket server (ESOCK) and the serial comms server (C32). ESOCK provides clients with a BSD sockets-like interface to server-side protocol functionality that resides in framework libraries called protocol modules (PRTs). Currently, the TCPIP and the IrDA protocol suites are implemented as protocol modules.

C32 provides clients with an RS232 serial interface to serial port functionality which is implemented in framework libraries called comm server modules (CSYs). Serial port emulation over IrDA sockets is provided by IrCOMM.CSY. Asynchronous requests are handled internally in these components through lightweight active objects, a Symbian OS construct which obviate the need for multithreading within the server.

Symbian OS Bluetooth® wireless technology architecture

The Bluetooth® wireless technology profiles were the key initial drivers for Symbian OS Bluetooth® wireless technology implementation. Symbian OS Version 6.1 Bluetooth® stack is designed around supporting the Generic Access Profile, the Serial Port Profile and the Generic Object Exchange Profile. Key design goals included:

The ability to run multiple simultaneous logical connections to multiple remote devices.
The separation of the protocol stack from the security policy as suggested by the Bluetooth® Security White Paper [1].
The ability to support any specification compliant hardware through the Host Controller Interface.
From the outset use case analysis was used to map required Bluetooth® wireless technology profile support to system features.

In the Symbian OS Bluetooth® architecture, core stack functionality is implemented by two components, HCI.DLL and the Bluetooth® protocol module (BT.PRT). The Host Controller Interface module encapsulates the canonical set of HCI commands and events. Currently the serial UART flavor of HCI has been implemented using the Ericsson Bluetooth® Development Kit, the DigiAnswer PCMCIA cards and most recently the Cambridge Silicon Radio Casira modules as reference hardware. Symbian is, however, able to support any HCI-compliant Bluetooth® wireless technology hardware through a modular Host Controller Transport Layer architecture.

BT.PRT encapsulates the Bluetooth® L2CAP and RFComm layers. As a Symbian OS protocol module, it provides a sockets API to these protocols. BT.PRT furthermore spawns distinct Bluetooth® Manager and Service Discovery Protocol (SDP) server threads. The Bluetooth® Manager abstracts all User Interface interactions and access to non-volatile storage. This allows for a future implementation of flexible access policies to the range of services supported by a Symbian OS phone. The SDP server handles SDP queries and responses. Serial port emulation is supported by the Bluetooth® comm server module (BTCOMM.CSY) module which provides a number of thin virtual serial ports for different legacy services running over RFCOMM socket functionality.

Development evolution

Symbian OS Bluetooth® wireless technology will evolve as follows:

Pre-Qualification against the v1.1 Bluetooth® wireless technology Specification.
Symbian OS OBEX server implementation to replace existing static library.
Bluetooth® 2.0 support through the addition of an ad-hoc networking interface (IP over Bluetooth® Network Encapsulation Protocol (BNEP) over L2CAP).
Additional profile support.

The existing framework components will be enhanced to implement this support but the basic stack APIs will not change. The addition of ad-hoc networking via Bluetooth® wireless technology is a particularly exciting area as it represents a genuine paradigm shift in mobile computing, ushering in a new range of services. Symbian OS is well-positioned to handle the transition to this world of Personal Area Networking and offers mobile phone maunufacturers unique advantages. Support for Bluetooth®wireless technology has been designed into the core platform from the outset.